1. Field of the Invention
The present invention relates to a fuel injection apparatus in which a fuel injector is mounted on an internal combustion engine through a cylinder screw.
2. Related Art
It is known to use a cylinder screw for mounting a fuel injector on a cylinder head of a direct injection type engine in which fuel is injected directly into an engine cylinder. The cylinder screw is fitted around the outer periphery of the injector. The cylinder screw is threaded into the cylinder head to press the injector to the cylinder head.
As the nozzle part of the injector faces a combustion chamber according to the injector in the above direct injection type engine, however, soot and similar substances produced in combustion are likely to accumulate between the nozzle part and the cylinder head and stick thereat. When the soot and similar substances remain sticking strongly, the injector must be shaken or pried to be detached from the cylinder head by using certain tools after unthreading the cylinder screw from the cylinder head, resulting in difficult in detaching work.
Further, it may occur that the force applied to the injector deforms members constituting the magnetic circuit of the injector or varies the biasing force of a spring, resulting in changes in injection characteristics of the injector, i.e., fuel injection timing and fuel injection quantity. Thus, it becomes impossible to reuse the injector which has been detached once.
It is also known by the publication ("DIESEL FUEL INJECTION", page 159, FIG. 4.108(C), published on Jun. 15, 1988 by SANKAIDO) to mount an injector on a cylinder head without turning the injector. This injector may be attached by holding a flange by the cylinder head and a retaining nut, and by the retaining nut or the like a fuel pipe may be attached to the injector having been attached to the cylinder head. As a large turning force is exerted on the injector at this moment, the injector must be gripped firmly by a certain tool to hold the injector in position to the turning direction for such attaching work. This will complicate the injector mounting work.
Further, as the large turning force is applied to the injector for a thread engagement between the retaining nut and the injector at the time of connecting the fuel pipe to the injector, the position of the injector is likely to be displaced in the turning direction even if the injector is held gripped by the tool.
Still further, a cylinder screw is threaded into the cylinder head until it abuts the retaining nut for pressing the injector to the cylinder head. The injector is pressed to the cylinder head at an end position of the threaded engagement part between the housing and the retaining nut which is opposite to the injector attaching direction. According to this attachment structure, the distance between the position where the retaining nut is engaged with the cylinder head and the position where the retaining nut is pressed by the cylinder screw becomes long, increasing the deformation of the retaining nut by the tightening force of the cylinder screw. The increase in the deformation of the retaining nut increases the deformation of the injector constituting members, particularly, the deformation of members located within the axial length of the retaining nut. Therefore, if this attachment structure is applied to an electromagnetically-controlled injector, the air gap between a movable core and a stationary core may be shortened, a sliding clearance of movable parts may be reduced or fixing condition between members may be weakened. The deformation in the injector will cause changes in injection quantity and injection timing of the injector, making it difficult to provide the injection characteristics as designed.